Objective To analyze the differential expressed genes(DEGs)in the lung tissues of rat model of high altitude pulmonary edema(HAPE)by using microarray analysis in order to provide new clues for molecular mechanism of HAPE.Methods Healthy male SD rats(8 weeks old,weighing 200±20 g)were randomized into normoxia control(NC)group,lipopolysaccharide(LPS)group,hypoxia group and hypoxia+low-dose LPS(HL)group.The rats of the LPS group and HL group were injected with 0.1 mL 0.05％LPS per 100 g body weight,and those of the NC group and the hypoxia group were administered with an equivalent volume of normal saline.The rats of the hypoxia group and the HL group were housed in a hypobaric chamber simulating an altitude of 5 000 m,and those of the NC group and the LPS group were raised simultaneously outside of the chamber.The wet/dry mass ratio(WDR)of lung tissue and total protein content in bronchoalveolar lavage fluid(BALF)were measured,and the histopathological changes of lung tissue was observed using HE staining.The total RNA was extracted from the lung tissues,and the mRNA expression profile was obtained with Affymetrix microarray followed by Gene Ontology(GO)analysis and Kyoto encyclopedia of genes and genomes(KEGG)pathway analysis with Metascape(http://metascape.org).Results The rats of the HL group showed significant congestion,edema,and widened alveolar septa.Compared with the NC group,the HL group had significantly increased lung WDR(P＜0.01)and total protein content in BALF(P＜0.05).Gene expression analysis revealed that there were 79 genes up-regulated and 59 genes down-regulated in the hypoxia group,473 genes up-regulated and 695 genes down-regulated in the LPS group,and especially,669 genes up-regulated and 1 253 genes down-regulated in the HL group.GO and KEGG pathway analyses revealed that the upregulated genes in the HL group were mainly enriched in biological processes,such as cytokine mediated signaling pathways,response to IL-1,regulation of inflammatory response,as well as signaling pathways,including cytokine-cytokine receptor interactions,TNF,NF-κB,IL-17,complement and coagulation cascades,etc.The down-regulated genes were mainly enriched in biological processes,such as extracellular matrix organization,regulation of endothelial cell migration,cell substrate adhesion,as well as signaling pathways,such as focal adhesion,Wnt,cGMP-PKG,PI3K-Akt,Rap1,etc.The mRNA expression of NF-κB,TNF-α,IL-1βand IL-6 was significantly up-regulated in the lung tissue of the HL group(P＜0.01).Conclusion Hypoxia+low-dose LPS is an effective procedure to establish a reliable model for HAPE in rats.Hypoxia can significantly aggravate LPS-induced inflammation and immune response,enhance the expression of inflammatory mediators,and thus promote the pathogenesis of HAPE.